Though there are many quantitative and qualitative techniques employing the physical and general chemistry to assay precious metals, these are all too sophisticated for most jewelers. For example, a method employed by most jewelers to determine the purity of the gold alloy is to use a series of standard gold pencils and compare the results of a scratch test using said pencils with a gold specimen to be assayed. In such a technique, the jeweler has gold rods of 8 karat, 10 karat, 12 karat, 14 karat, 16 karat, and 18 karat composition and an abrasive stone. He scratches the gold specimen under test on the stone and adjacent to that scratch he scratches the gold pencils on said stone. After treating the stone with an acid and comparing the color of the specimen scratch with the color of the gold pencil scratches, he visually estimates the quality of the specimen in karats. This highly inaccurate system is strongly dependent on the technique and ability of the jeweler employing the test. In contrast, the proposed invention employs the latest electronic devices to make a chemically dynamic test of the purity of precious metals. Operator technique is a minor consideration. The proposed invention uses electro-chemistry in combination with current metering and time dependent circuits in a simple hand-held device. The anode of this electro-chemical system is the material under test and the cathode is the reference material. A metered current causes an electro-chemical reaction at the anode and after the current-induced electro-chemical reaction is terminated, the electromotive force is monitored as a function of time. The time dependent decay of the potential difference of the cell so created is indicative of the purity of the precious metals under test. Though the embodiment of the proposed system is to assay gold, it has been determined that the same technique can be used for alloys of other precious metals. The system is self-contained and uses an acid-filled syringe for testing which also contains the reference cathode. Said syringe is wired to control electronics which has appropriate circuitry for accurately metering a current and activating electronic switches to terminate said current and to monitor the potential decay. In addition, the electronics has micro-processors and memory circuits to conveniently operate either an analog or digital display indicating the purity in units of measure familiar to the operator.